William Playfair has the kind of biography that seems fictional. He worked for James Watt (steam engine pioneer and namesake of the watt), helped to storm the Bastille (one of the most symbolically significant events of the French Revolution), and – yes – invented the hated pie chart, the bar chart, and the line chart.

(Why is the pie chart hated? It’s difficult to compare quantities represented in pie charts because they rely on area rather than length, and it’s harder to compare area visually.)

The original pie chart is pictured above; it was first published in Playfair’s 1801 book Statistical Breviary. It shows the proportion of the Ottoman Empire that lay in Africa, Asia, and Europe at the time. For this and his earlier work Commercial and Political Atlas, he is considered one of the founding fathers of data visualisation.

But it turns out that Playfair was also keen on espionage. Although he helped to storm the Bastille he later developed a hatred for the French revolutionary government, and proposed a scheme to bring it down. And it kinda worked.

In the late 18th century the French National Assembly had issued currency called assignats. Well, originally they were bonds but then in 1790 they became legal tender instead. Playfair proposed that the British forge as many assignats as possible in order to devalue the currency and crash the French economy. He was not alone: supposedly the Belgians and the Swiss had the same idea. The assignats lost so much value that trade and manufacturing in France suffered. The economy did not implode, but it was severely damaged.

So there you have it: pie charts and espionage. Who would have thought it?

She did, and probably contributed more to the modern adoption of the pie chart than Playfair. I don’t know if there’s evidence she ever saw Playfair’s version, so it could have been yet another case of simultaneous discovery.